1. Field of the Invention
The present invention relates to an electric element breakdown detector and, more particularly, to a circuit which produces a signal when an electric element, such as a coil or a light emitting diode (LED), breaks.
2. Description of the Prior Art
In the electric appliances, such as a copying machine, many electric elements are provided. Taking an example of a copying machine, the electrical circuit of the electromagnetic clutch is employed to control the reciprocating movement of the platform carrying an original document. The electromagnetic clutch has a solenoid coil which is connected in a manner shown in FIG. 1. One end of electromagnetic coil 1 for driving the clutch is connected to the power source (+VB), and the other end thereof is connected to transistor 2 and further to ground. Transistor 2 serves as a switching element. In the above arrangement, when transistor 2 is disabled, a counter electromotive force is generated across electromagnetic coil 1, which may cause a serious damage of transistor 2. To protect transistor 2 from receiving such a voltage, a diode D serving as a voltage dropping element is connected parallel to the electromagnetic coil. Thus, the counter electromotive force generated across electromagnetic coil 1 is absorbed in the diode, thereby preventing transistor 2 from being damaged by the counter electromotive force.
Furthermore, as shown in FIG. 2, when a relay switch 3 is connected in series with electromagnetic coil 1 in lieu of the transistor 2, the counter electromotive force is also absorbed in the diode D so that an electrical discharge will take place between the contacts a and b of the switch 3, and thereby preventing the contacts from being damaged, and also the the generation of noise signals can be eliminated.
In the prior art copying machine, if the platform makes an erroneous movement, it is understood that something is wrong, but it is very difficult to spot the place where the error exists. Sometimes it is not possible to discriminate the place immediately whether the failure is really due to the breakdown of the coil, or whether it is due to some other factor. Thus, much time and labor are required to repair the failure.
The above problem exists not only with the coils but also other electric elements, such as an indicator employing a lamp, a light emitting diode or the like.
Furthermore, the present invention is applicable not only to the copying machine, but also to any machine which employs an electric circuit.